Theses and Dissertations from UMD
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Item TIME-SERIES FOCUSED ASSESSMENTS OF CHANGING MARINE BIVALVE COMMUNITIES IN THE BERING AND CHUKCHI SEAS(2021) Goethel, Christina; Grebmeier, Jacqueline; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Pacific Arctic has been experiencing rapid environmental change, including increasing bottom water temperatures, declining sea ice extent, and ecosystem shifts. In the northern Bering Sea (NBS), bottom water temperature was ~1.5°C higher in 2018 than previously recorded. Temperature and sea ice dynamics could alter this benthic-dominated system, potentially shifting the food web to a more pelagic-dominated system. Bivalves, a key component of the benthic macrofaunal community, are important prey items for the spectacled eider in the NBS and for walrus in both the NBS and the southeast Chukchi Sea (SEC). Here, data were collected and analyzed at established time-series stations in the NBS and SEC as part of the Distributed Biological Observatory. The objective was to evaluate changes to bivalve communities, and how those relate to overall benthic community shifts and functioning. By using both time-series and experimental techniques my research: 1) evaluated past trends in detail for a single dominant clam species, Macoma calcarea, 2) tracked the abundance, biomass, and dominant size class of two dominant bivalve species, M. calcarea and Serripes spp., from 2015-2019 when drastic physical changes have been observed, and 3) scaled up connections amongst the individual biological responses to full macrofaunal community population responses to the composite environmental changes using shipboard sediment community oxygen consumption (SCOC) incubation and individual respiration experiments. Results indicate that bottom water temperature and food availability (measured using sediment chlorophyll-a inventories as a proxy) play the largest role in controlling the population dynamics of M. calcarea, and that the population is contracting northward in the NBS. In the SEC, results suggest a shift in the hotspot of M. calcarea from station UTN5 (north) to UTN2 (south). However, size class results showed a larger number of smaller clams in the south and a smaller number of larger clams further north, indicating the biomass hotspot likely remains at UTN5. Serripes spp. were prevalent in 2014-2017, but started to decline in 2018 and 2019. Experimental results demonstrated increased SCOC and individual oxygen consumption in higher temperatures, but that there was little effect to oxygen consumption when food was added.Item The significance of sea ice algae in the Pacific Arctic determined by highly branched isoprenoid biomarkers(2021) Koch, Chelsea Wegner; Cooper, Lee W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our current understanding of ice algae as a carbon source at the base of the Arctic food web is limited because of difficulties unequivocally distinguishing sympagic (sea ice) from pelagic primary production once assimilated by consumers. For this study, I tested the utility of highly branched isoprenoids (HBI), which are unusual lipids produced by diatoms. This includes a biomarker found exclusively in Arctic sea ice termed the ice proxy with 25-carbon atoms (IP25) and two other HBIs with sea ice and pelagic sources. HBI measurements in the Pacific Arctic (the northern Bering and Chukchi seas) were sparse compared to the rest of the Arctic prior to this investigation. Analysis of surface sediments and cores collected across the continental shelf revealed a latitudinal gradient of increasing sympagic HBIs. Some of the highest concentrations of IP25 recorded in the Arctic were found in the Chukchi Sea. Fluxes of IP25 indicated year-round export of ice algal lipids in this region. Persistent diatom fluxes and rapid burial of sympagic carbon are likely a sustaining resource for infaunal communities throughout the year. As such, HBIs were measured in benthic primary consumers and indicated an elevated utilization of ice algae by surface and subsurface deposit feeders, while suspension feeders by contrast showed greater pelagic organic carbon utilization. Sympagic organic carbon signatures were largely influenced by the HBI content in local sediments. This led to the identification of two species with possible dependencies on ice algae. This method was extended to transient, higher trophic organisms by measurement of HBIs in Pacific walrus livers harvested during subsistence hunting activities. Relative HBI proportions were shown to relate to foraging location and revealed a higher reliance on sympagic organic carbon by female and juvenile Pacific walruses relative to males. This is likely due to a greater requirement for sea ice habitat by females and calves in the Bering and Chukchi seas. This study showed that HBI biomarkers can robustly track sea ice organic carbon contributions through the Pacific Arctic food web and should be considered alongside other trophic markers in future monitoring efforts in response to climate change.Item An evaluation of methods for measuring phytoplankton and ecosystem status in the Chukchi Sea(2020) Neeley, Aimee Renee; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation represents a three-pronged approach for evaluating ecosystem-level changes in the Chukchi Sea: 1) evaluation of uncertainties in field measurements of absorption 2) direct measurements of phytoplankton taxonomy and the community’s interaction with the environment and 3) apply existing and new remote sensing tools to measure ecosystem-level changes over large spatio-temporal scales. The first and final chapters provide context for the dissertation and conclusions. The second chapter quantifies the magnitude of uncertainty within multiple methods for measuring particle absorption. The light field exiting the surface ocean is measured by satellite instruments as ocean color and is impacted by water column absorption. Biogeochemically-relevant products, such as phytoplankton and particle absorption are derived from the light field using algorithms. Therefore, accurate measurements of absorption are critical to algorithm development and validation. I employed a multi-method approach to estimate the precision of measuring optical density of particles on a filter pad using two common spectrophotometric methods, and assessed the uncertainty of the computational techniques for estimating ap. The uncertainty ranged from 7.48%-119%. Values of ap at 555 nm and 670 nm exhibited the highest values of uncertainty. Poor performance of modeled ap compared to measured ap suggests the uncertainties are propagated into bio-optical algorithms. The third chapter investigates the consequences of earlier seasonal sea ice retreat and a longer sea-ice-free season on phytoplankton community composition. The timing of sea ice retreat, light availability and sea surface stratification largely control the phytoplankton community composition in the Chukchi Sea. This region is experiencing a significant warming trend, decrease in sea ice cover, and a documented decline in annual sea ice persistence and thickness over the past several decades. I applied multivariate statistical techniques to elucidate the mechanisms that relate environmental variables to phytoplankton community composition in the Chukchi Sea using data collected during a single field campaign in the summer of 2011. Three phytoplankton groups emerged that were correlated with sea ice, sea surface temperature, nutrients, salinity and light. The fourth chapter evaluates a new remote sensing tool for its utility to trace trends in ocean color over the summer months, 2003-2018, in the Chukchi Sea. The apparent visible wavelength reduces an ocean color spectrum to one number that represents the apparent color of the water. Median trend analysis of apparent visible wavelength and Chlorophyll a indicated that an ecosystem-level change in phytoplankton and nonalgal particles has occurred, correlated with the loss of sea ice.Item QUANTIFYING VARIABILITY OF BLACK CARBON TRANSPORT FROM CROPLAND BURNING IN RUSSIA TO THE ARCTIC DRIVEN BY ATMOSPHERIC BLOCKING EVENTS(2017) Hall, Joanne Vanessa; Loboda, Tatiana V; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Short lived aerosols and pollutants transported from northern mid-latitudes have amplified the short term warming in the Arctic region. Specifically, black carbon is recognized as the second most important human emission in regards to climate forcing, behind carbon dioxide with a total climate forcing of +1.1Wm-2. Studies have suggested that cropland burning may be a large contributor to the black carbon emissions which are directly deposited on the snow in the Arctic region. However, accurate monitoring of cropland burning from existing active fire and burned area products is limited, thereby leading to an underestimation in black carbon emissions from cropland burning. This dissertation focuses on 1) assessing the potential for the deposition of hypothetical black carbon emissions from known cropland burning in Russia through low-level transport, and 2) identifying a possible atmospheric pattern that may enhance the transport of black carbon emissions to the Arctic. Specifically, atmospheric blocking events present a potential mechanism that could act to enhance the likelihood of transport or accelerate the transport of pollutants to the snow-covered Arctic from Russian cropland burning based on their persistent wind patterns. This research study confirmed the importance of Russian cropland burning as a potential source of black carbon deposition on the Arctic snow in the spring despite the low injection heights associated with cropland burning. Based on the successful transport pathways, this study identified the potential transport of black carbon from Russian cropland burning beyond 80°N which has important implications for permanent sea ice cover. Further, based on the persistent wind patterns of blocking events, this study identified that blocking events are able to accelerate potential transport and increase the success of transport of black carbon emissions to the snow-covered Arctic during spring when the impact on the snow/ice albedo is at its highest. The enhanced transport of black carbon has important implications for the efficacy of deposited black carbon. Therefore, understanding these relationships could lead to possible mitigation strategies for reducing the impact of deposition of black carbon from crop residue burning in the Arctic.Item A Proteomics Approach to the Examination of Proteins in Marine Systems(2014) Faux, Jessica Felicia; Harvey, Henry R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The response of global carbon and nitrogen cycles to future climate change is uncertain. In order to understand the impacts that future changes to climate will have on these cycles, a more detailed understanding of them is essential. This dissertation utilizes a combined approach of molecular biomarkers and proteomic investigations to elucidate historic source material contributions and microbial protein production to contribute to a more thorough understanding of the marine carbon and nitrogen cycles. The examination of molecular organic biomarkers throughout an Arctic sediment core showed the dominant input in the area was from marine sources with lower but steady contributions from terrestrial sources during the Holocene. Attempts to recover proteins from deeper sediments to correlate with lipid biomarkers were unsuccessful but led to the optimization of an extraction protocol for an added protein standard, bovine serum albumin, from sediments. An investigation into the expressed proteome of the heterotrophic marine bacterium, Ruegeria pomeroyi, under environmentally realistic carbon supply conditions during exponential and stationary growth phases identified over 2000 proteins. The most abundant proteins identified were responsible for porins, transport, binding, translation, and protein refolding and could represent potential biomarkers of bacterial processes and/or activity. A parallel study of R. pomeroyi, in which 13C-labeled leucine was added to the culture during exponential growth phase, showed labeled incorporation ranging from 16 to 21% of the total proteins produced depending on growth phase. The widespread distribution of the label among the growth phases indicates active recycling by the bacteria. This study demonstrates a method through which bacterial protein synthesis can be tracked. A study of the marine diatom Thalassiosira pseudonana acclimated to iron replete or iron-limited conditions showed iron-limited organisms increased proteins involved in pathways associated with intracellular protein recycling, the pentose phosphate pathway, lower photosynthetic energy production, enhancement of photorespiration, and increased polysaccharide production. This application of proteomics to the examination of proteins in marine sediments, a marine diatom, and a heterotrophic marine bacterium shows the potential for these techniques to help elucidate the fate of proteins in marine environments and could be used in conjunction with well-established molecular organic marker studies.Item COMPOUND SPECIFIC CARBON ISOTOPE ANALYSIS FOR BIOMARKERS ASSOCIATED WITH MARINE METHANOTROPHY IN THE ARCTIC(2012) Dougherty, Mara Ryan; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A large reservoir of methane exists in marine sediments. The fate of methane is of particular concern in the Arctic, a region that has already demonstrated sensitivity to climate change. The removal of this potent greenhouse gas from the carbon cycle is largely mediated by microorganisms. In methane bearing ocean sediments where sulfate penetrates the surface sediment, sulfate reducing bacteria (SRB) and archaeal methanotrophs are found and believed to act as a consortium in the anaerobic oxidation of methane (AOM). Despite efforts based on thermodynamic models, rate measurements, and δ13C analysis of microbial biomarkers, the process by which methane is removed from anoxic sediments remains speculative. Sediment samples were collected from the Beaufort Shelf, east of Point Barrow, AK as part of the Methane in the Arctic Shelf/Slope (MITAS) Expedition in 2009. Core PC13 from this cruise was selected for compound specific carbon isotope analysis due the measured sulfate and methane concentrations. Stable carbon isotope analysis of the bacterial biomarkers selected specifically for known SRB phylotypes associated with AOM (i.e., i-C15:0, ai-C15:0 and C16:1 fatty acid methyl esters) resulted in δ13C values ranging from -27.8 to -25.3 /, strongly 13C-enriched relative to the biogenic methane in this core (δ13C = -100.0 to -74.6 /). At AOM sites, the microbial community involved in the process should reflect the carbon isotopic signature of the methane in instances of methanotrophy. In PC13, the bacterial biomarkers were not 13C-depleted like the methane, suggesting the lack of sulfate dependent AOM. The measurement of sulfate reduction rates and phylogenetic investigations corroborated the result from biomarker analysis, that the primary pathway for methanotrophy at this site is not coupled to sulfate reduction. Radiocarbon analyses of the bacterial biomarkers from PC13 were not utilized for the determination of methanotrophic pathways because the biomarkers targeted were for phylotypes whose dominant function at this site is not coupled to methanotrophy. However, the radiocarbon age of the bacterial markers may be useful in determining the sediment deposition rate at this site. For these biomarkers at 396 and 516 cm below the seafloor, the radiocarbon ages are 5805 and 5878 radiocarbon years, respectively. These ages result in an offset of 2500 radiocarbon years older relative to the shell fragments analyzed from the same depth. The biomarker age likely represents the older sediment delivered to the western Arctic via current systems, while the age of the shell fragments were deposited contemporaneously.Item CALORIC CONTENT OF BERING AND CHUKCHI SEA BENTHIC INVERTEBRATES(2012) Wilt, Lisa Marie; Grebmeier, Jacqueline M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Extensive seasonal sea ice reduction has highlighted the need to evaluate the status and potential long term changes of highly productive benthic communities in the Pacific Arctic Region. Walrus that use sea ice to access offshore feeding areas are now being forced to haul out on land for part of the year, requiring them to forage for benthic prey from closer to shore. To explore this energetic problem, I conducted a caloric survey of benthic invertebrates, and evaluated relationships between caloric content and environmental variables. Latitude was the strongest non-taxonomic dependency for caloric content (ANOVA p=0.003 with taxon dependencies, p<0.001 without). Cluster analysis revealed caloric densities were higher in offshore, high nutrient Bering Sea Anadyr Water, and lower in nearshore, low nutrient Alaska Coastal Water. An evaluation of preservation techniques indicated formalin fixation increased infaunal caloric content (p<0.001), suggesting caution while converting traditional benthic population studies to caloric values.